1. Field of the Invention
This invention relates to a method of masking bodies to prevent the adhesion of a tightly adhering, vapor deposited, comformal coating on selected portions of the body.
2. Description of the Prior Art
Vapor deposition coatings are known to be applied to various workpieces. The chemistry of certain coatings such as the polymer coatings formed from the condensation of vaporous diradical materials such as the P-xylylene monomers makes them unique, tightly adhering conformal polymer coatings having a molecular weight of approximately 500,000. Once these materials condense on the workpiece they are not only totally conformal and tightly adhering but very tenacious since they are also very chemical resistant.
These very properties that make such coating desirable also cause difficulties where only certain areas of the workpiece is to be coated. In the past the coating on selected areas were either mechanically removed after coating by brushing, scraping, peeling or the like or were mechanically masked prior to coating.
One mechanical masking technique is taught in U.S. Patent 3,895,135 issued July 15, 1976, to P. Hofer. This patent describes a complex mechanical masking process in which that portion of the surface of the body which is not to be coated is masked so as to provide a constricted flow path for the vapors of the material being deposited. This constriction is claimed to create, along the interface between the masked and unmasked portions of the substrate, a relatively thin region in the deposited coating at the end of the flow path. This thin region was then used as a tearline so that upon mechanical removal of the masking means the coating would tear along this line and be removed along with the mask.
However it has now been found that when such materials are deposited in a deposition chamber maintained at an operating pressure in the order of 100 millitorr or less that the vapor is so highly penetrent that it will coat an area normally inaccessable and will in fact penetrate under masks mechanically held on the surface of a workpiece.
Moreover because of the small sizes of integrated circuits and particularly because of their detailed complexity, mechanical masking means have not been found to be suitable.